In a commonly used process for electrophotographic printing applications, such as for printers and copiers, a uniform charge is applied to a photoconductive surface on a drum or belt. A light beam, such as from a laser, is used to expose the surface, leaving an electrostatic latent image corresponding to the image to be printed. The latent image is developed by the application of toner particles that adhere to the electrostatic latent image. The toner image is transferred to the media intended to receive the printed image, and the toner image subsequently is fixed to the media through the application of heat and/or pressure in a fuser.
In printers, copiers, and other machines having sheet handling pathways, electrical charges can build up in media, such as paper, that is transported through the machine. The media transported through such a device, both before and after reception of the toner image thereon, is frictionally contacted by numerous rotating members, and is slid along, over and against various stationary guide members. Consequently, the media can accumulate both positive and negative electric charges, both as a result of transport through the machine and from transfer of chargers in the electrophotographic process. Paper will typically accept and hold such charges readily.
Machine performance and function are adversely impacted by the buildup of charges in the media. Charges in the media can cause the media to be attracted to or repelled from transport surfaces, interfering with proper transport and indexing of the media for proper printing. Charges in the media also can interfere with transfer of the toner image to the media surface, by attracting stray toner particles thereto, in areas of the sheet not intended to receive a toner image. Such charges also can cause sheets to attract each other, causing media jams in the machine.
Thus, it is desirable to remove the electrostatic charges from the sheet. It is known to use devices to ionize air surrounding the sheet, thereby providing a pathway to ground. It is also known to contact the sheet directly with conductive strips, providing a more physically continuous grounding path for charges on the sheet. Early known ionizing devices where expensive and produced ozone, and contacting devices sliding over a newly formed image on a sheet transported through the machine degraded the image quality. Thus, neither of these designs was completely satisfactory.
It also is known to contact the sheet with conductive brushes having fibers secured in a matrix. For example, it is known from U.S. Pat. No. 5,354,607 “FIBRILLATED PULTRUDED ELECTRONIC COMPONENT STATIC ELIMINATOR DEVICES” to form pultrusions from densely packed bundles of fibers. One end of the bundle is fibrillated, and the exposed ends thereof contact a surface to be discharged. Other types of both contacting and non-contacting brush-like static charge eliminators are known also.
In another known, brush-like static eliminator, a thin tape of aluminum foil is provided transverse to the paper path in a machine. A plurality of discrete bundles of individual electrically conductive fibers are adhered to the aluminum foil, and can contact or come in close proximity to the surface of a sheet transported along the path. A problem with this design is that aluminum foil can tear easily, and is difficult to apply on a machine in a straight line, which is necessary to maintain constant space from a sheet along the length of the device. It is also known to use an aluminum strip rather than foil. However, the aluminum strip has physical memory, and will tend to curve at the ends thereof, if the aluminum strip was ever provided or stored in a roll. Also, aluminum is subject to oxidation, which reduces the conductivity and increases the surface resistance. If oxidation is significant, the effectiveness of the static control device can be diminished.
Attempts at improving such devices have not met with total success. Using a non-conductor, such as polyester, in the support or carrier strip may eliminate memory problems, but requires incorporation of conductive structures for connecting the fiber bundles to a grounding source. A single fiber or a plurality of fibers running the length of the strip can be used as the conductive structure, but is subject to failure if the continuity thereof is broken. Providing a metal coating on a non-conductive base material to serve as the conductive structure is also effective electrically, but scratching can cause discontinuity and failure of the device.
Another problem has been encountered with such devices as machine architectures have become smaller. Smaller, lighter machines are desirable. To achieve this, frames are becoming increasingly thin and streamlined as machine profiles become smaller. Consequently, surfaces to which an anti-static device can be attached are becoming thinner, and narrower carrier strips are needed in the anti-static devices. Attachment of the very thin fibers to a narrow carrier strip has become problematic.
What is needed in the art is a rigidly backed static eliminator that has bulk conductivity and corrosion resistance, facilitates straight installation of the device in a printer, copier or the like and can be made relatively narrow for installation on thin surfaces.